It is well established in the art to produce ophthalmic lenses, more specifically hard and soft contact lenses, in an automated manufacture process with reusable molds. In mass production of contact lenses, specifically so-called disposable lenses, a large number of contact lenses must be manufactured in a relatively short period of time. In an advantageous method of mass production, a lens forming material, e.g., a polymer or prepolymer solution is introduced into a female mold half, the casting mold is closed by the respective male mold half and then the lens forming material is polymerized and/or cross-linked e.g. with ultraviolet (UV) light. Such mass production of contact lenses, which is usually performed in a closed loop process, is described, e.g., in WO 98/42497. Suitable polymers formed by photochemical polymerization of suitable prepolymers include polymers based on polyvinyl alcohols (PVA) or silicone hydrogels (SiHy) as well as based on polyethylene glycols (PEG).
During the UV light induced polymerization and/or cross-linking of the lens forming material within the molds the UV light in the respective zones which are outside of the areas required for contact lens production is masked. Thus, due to this spatial limitation of the irradiated UV light only the unmasked portion of the lens forming material in the mold cavity is hardened, whereas excess material e.g. in an overflow region or area of the mold may remain attached to the lens as “flash”. In order to obtain fault-free lenses these residues of non-polymerized and/or non-cross-linked lens forming material, the “flash”, must be separated from the molded lens. This separation is supported by a proper sealing of the mold halves and by a very careful shaping of the mold separation planes, in particular in the edge region of the mold cavity which defines the lens edge. The automated manufacture process is also called “full mold process”because there is no working of the lens edge required after the molding of the lens.
In order to separate the flash from the molded lens in a known manufacture process the mold is opened by moving the mold halves away from each other. The non-polymerized and/or non-cross-linked lens forming material is then flushed away from the mold halves with a jet of a flushing medium, usually water or a solvent, such as, e.g., propanol, isopropanol or the like. Subsequently the molded lens is dried, e.g. by subjecting it to a warm air flow. Most lens forming materials during polymerization and/or cross-linking have a tendency to shrink to a certain—small—extent. Because of the shrinkage a negative pressure builds up within the mold cavity which may hamper the opening of the mold such, that an increased effort is required for the opening. During the opening of the mold and during the flushing some of the non-polymerized and/or non-cross-linked material may reach the exposed surface of the molded lens and may adhere thereto and soil the lens. Thus, very thorough surface cleaning steps for the lens surfaces should be provided in subsequent process steps.
It is therefore an object of the present invention to provide a method by which excess lens forming material, which is non-polymerized and/or non-cross-linked, may reliably be separated from the molded lens. A soiling of an exposed surface of the molded lens, whether during opening or during flushing of the mold halves, shall be avoided. Further, a method shall be provided which facilitates the opening of the mold.